Peter - once again, I continue to be both moved and honored by the critical reading of my work. I also feel quite lucky that, through Aikiweb, I can respond in a way that one cannot in usual printed material.
I do not assert that anyone who went through what Takeda "went through" would end up like Takeda. Instead, only Takeda could end up like Takeda. The observation of horror, independent of culture, does cause one's character to develop, in general, along certain lines. But this does not guarantee the "development of a Takeda." The majority of warrior cultures are typified by distant fathers, a coming of age where one is separated from the feminine, initiation ceremonies that define, clearly and harshly, the masculine role, and very often, de-sensitization procedures so that one is at ease with violence. This set of components would explain the creation of the samurai class, for example - and a wonderful example of this is described in Junichi Saga, Memories of Silk and Straw: A Self-Portrait of Small-Town Japan, 1987, Kodansha International, a book you cite. I do not have the book at hand, but one chapter describes a former executioner of a han, the grandfather of the narrator. He is a very severe man who goes duck hunting in the following manner: He takes a musket and a small lead smelter. At the riverside, he smelts a single lead ball. Loads his musket. Shoots a single duck. Returns home.
I consulted with some film makers in Africa on the making of a documentary on the boy soldiers - what is remarkable is that, many, now returned home, are such gentle souls. I've met some in my area - they are attendants in a mental hospital, and the most patient, kind staff in the entire facility. But when one of them met me, me wearing BDU's (the many pocketed pants sometimes favored by military), he went into a mild flashback, only alleviated when I assured him that I liked the pants for the many pockets, not that I was a military guy.
With Takeda Sokaku, we do not have the same kind of man - a rigidly controlled warrior. Nor do we have the returned child soldiers - often gentle men who survive by deliberately "not remembering." Why not? First, I believe we start with innate character. To take my own sons, each was born into my hands. And I would assert with complete confidence that they are fundamentally unchanged from that moment - they were born with soul. The way they greeted the world is still the way they live. Takeda Sokaku was a ferociously independent being, defiant of authority. He had several significant disruptions of attachment - fostered to Dengoro Kurokochi's and then left alone/abandoned near a battlefield. (I shan't repeat the thesis of my chapter) - but in short, I am saying the "obvious" - Takeda Sokaku's life made Takeda Sokaku. Flamboyant, paranoid, and at the same time, passionate and desiring contact with others.Yet, I am not out of line in referring to what Sokichi did to his son as torture. Torture is the deliberate infliction of pain and destructive psychological experience. It can be done for sadism and it can be done for education. I don't care what your culture is - being involuntarily forced to experience severe pain - against one's wishes - with no way of making it stop - is, as Jean Amery, a holocaust survivor writes, always a rape of the body. With different cultural memes, that pain/torture may be "assimilated" differently, but it is still torture.
What is most significant to me is that Takeda found it necessary, as an adult, to point it out. One several occasions. What is significant is that he cut his own father out of his "lineage" of Daito-ryu.
I want to make it clear - unlike most others, I believe, I do NOT believe that Takeda Sokaku was impaired to the point of psychological pathology. But I also do not believe he was typical of his class and his times. He reminds me very much of the Araki-ryu admonition that one must be like a pine tree growing on a cliff. (The implication is that however the wind blows, however impoverished the root bed of rock and earth, you will, twists and all, grow up strong).
One of the "mysteries" of my work with youth is this - a life story can explain THAT child's life - but in many cases, cannot explain in general terms, chidren's lives. One of my best friends experienced horror in levels equal or greater to that we read of Takeda. He's not a man you would want to make angry - and fighting him would be a terrible mistake. But he is a loving father and husband and good friend. Abuse and violence are not like train tracks that lead to a pre-determined direction. Instead, they are blows that knock one OFF the rails - each of us will struggle through the swamps to our own destination - which is a combination of luck, character, and maybe the size of our feet.

A couple of other issues:
I did not rely on the account of Takeda's sumo as an old man to substantiate my belief that he learned the skills young (Heck, it's possible that Hisa was just being kind to his teacher and tanking, for all I know). I've done some provincial sumo when I was in Japan. I was at the peak of my physical strength, well over 200 pounds, and tough locals, with some real skill and lots of power, handled me easily. What catches my attention about Takeda is that he was a young teen, probably somewhere between 100-130 pounds, most likely on the lighter side of that range, and he was defeating such work hardened men whose family well-being would be impacted by victory or defeat. And he beat them all! That's remarkable. Hence, my conclusion that he must have known something more than a good uwatenage and some skillful tsuppari.

As always, I not only think most of your questions and critiques are valid - particularly in the demand for sources, more scholarly rigor and in catching a number of "jumping off points" for further writing and research. My goal, as always, is to knock the narrative off the rails - so something new might be found in the swamps I lead you.
My work as an assessor in child abuse cases actually runs quite parallel to this - very frequently, I'd be handed a case in which everyone had a slam dunk to taking a child away from parents - -or returning a child - and often I would knock the case right off the rails. Once in court, I would be questioned by both lawyers and, through them, other expert witnesses. My best work circled around noting what no one seemed to see about this particular child.
And that is what led me to ask how the scariest man in most aikido books was never violent to his students, but stabbed his own son, who surely learned from his father, but erased him from his own history, except to point out to others his lifelong damaged nails as his father's work.